Distinct counting a number of different columns in SQL Server

Question

I have a table containing order data as follows (simplified):

ID    CustomerID    OrderId
1     1             100
2     1             101
3     1             102
4     2             103
5     3             104
6     2             105

I want to write a query that collates all of the unique customerIds present in this table and counts the amount of orders that each customer has. But I'm struggling with how to go about this.

Select distinct customerId from table 

The above will give me all of the unique customerIds in the table, but then I'm not sure how to aggregate the counts of each customer's orders onto this data. Am I right in thinking it involves some kind of subquery?

Answer 1

You need COUNT and GROUP BY . Try like:

SELECT CustomerID,COUNT(*) FROM myTable GROUP BY customerID

Answer 2

You are describing group by :

Select customerId, count(*)
from table 
group by customerId;

This is a quite basic part of SQL syntax. You may want to brush up on your SQL.

Answer 3

Simple aggregation with group by clause :

select customerId, count(*) as orders 
from table 
group by customerId;